Recuperative apparatus



F. A. FAHRENWALD RECUPERATIVE APPARATUS Filed Nov. 28, 1924 4 Sheets-Sheet 2 .52 52." 27&

Frank A.Fc2. z rezzw'aZd S'ept.

`1,599,613 F. A. FAHRENWALD REGUFERATIVE APPARATUS 4'Shets-Sheet 5 Filed Nov, 28, 1924 4 Attorzze:

Sept. 14 1926.

* F. A. FAHRENWAL'D RECUPERATIVE APPARATUS' 4 Sheets-Sheet 4 Filed Nov. 28, 1924 Fab ren uraZd Frank A.

Fen x A FAHBENWALD, or CLEVELAND nexehes, OHIO.

BECUPEBATVB APZPAEATUS.

Aplicetion filed November 28, 1924:. Serial No. ?52,693

This invention relates to the production and maintenance of high temperatures by the combustion of fucl as employed in the reducton, smelting, and refini-ng of netals or the production and manipulation of glass, pottery, and other ceramic materials, the distillation of oils and oil shale, the production of power, and the performance of numerous Chemical reactions requiring high temperatures. The combustion of fuel entails &constant supply of fresh air and an equivalent discharge of combustion products, the former entering at the prevailing seasonal tem erature and' the latter escaping often at t e maximum temperature of the process. Sometimes the value-products of the operation are contained in the gases 'themselves as 'in distilling oil shale, sometimes the waste gases are largely valueless as in the chimneys of steam boilers and steel plants but in many cases the heat units carried by the escaping gas are suflicient to constitute the difi'erence between u financially profiteble and a financially unprofitable operation, and

in all processes of commercial magnitude the saving of waste heat is both sound practice economicaily and lucrative financially.

Many attempts have been made to effect this economy, usually by inducing the escaping gases to give up some of their heat unit-sto the entering air, thus decreasing the work necessary to be done by the action of fresh fuel but the ractical difiicultics are very great, especial y considering the high temperatures and enormous volumes of gases often encounter-ed.

Conside'ring for example, e blast furnace of a size which requires 'for its operation approximately 50,000 cubic' feet of air per min-- ute (approximately. two tons) delivered under a pressure of approximately ten inches of water. This air is delivered to the urnace by a pipe some three I feet in internal diameter, at a temperature from about '750 to 850 F. -The hotter it is to start with, the less coke is re quired in the urnace. Each increase of 100 .Blin thetemperature ofthisgair' is equivalent to approximately three' tons of coke per hour, andenables the saving of over 75 tons of coke alday. However, tor rea sons I shall. soon point out' it is not easy under present practice to mantin the 'tem .peroture steadily even at 1000 F. The chenictl Operations in such a blast .turhace result in the iieci arge,qtahoutgfiflfio paratus for elfecting this is only cuhic feet per minute of' a mixture of gases at from about 200` to 400 `F. (the balance being employed in heating the ore, evaporating the water it contains and reducing the ir'dh, which is a strongly endothermi process).

This blast furnece gas consists of approxinately: i

Per cent. Carbon monoxide 27 Cai-bon dioxide 12 Nitrogen 60 Hydrogen 1 The only Valuahle components are the carbon monoxideancl hydrogen, which, even after being coolecl to seasonal temperatures, have a combustion Value equivalent to approximately 24 tons of coke perhour. Af ter being cooled and washed about twothirds of this gas is burnecl under boilers or in engines while the remaining one-third which s equivalent to about 8 tons of coke per hour is burned to preheat the air which is fed to the blast furnace. The present'apabout ellicient: Half the amount would do equally well if it .could be thoroughly used, or the same amount would heat the entering air to a correspondingly higher temperature, thus saving coke in the furnace as first explained. It is or the particular purpose of saving a part of this 4 tons per hour loss that I have developed the particular devices hereinaftershown, although the same general appe'atus can be` applied to the saving of a considerable part of 'the waste heat containecl in the blsst furnace gas, and simple modifications of 'the epparatus equally fall ing within ;my invention can be utilized in other brnches of the arts. Great as this saving is; it is even less important than the saving in overhead costs which can beefi'ected bythe consequent speeding up the action of the blast furnace, and the elimination of labor and superintendence costs.

.l'n the establishing contemporary method each' blest furnace is sc'oompanied by four, upright, ative stores connected to the blast 'urnace, blower fans, waste stuck, and each other by a meze of heetinsulated piping and water cooled velvesf Each stove is filled with a checkerwork 'piie of refrectory brick exoept' for a fi ue in which the blastturnace gas is hurnecl, the products escapirg to 'the wsste stuck efter passing through the bricl worlt 2 i 1,599,e1s

. lutedwith cold air in order to fiaintan i'easonahly uniform conditions in the blast furnace. Tcward the end oi each blowing period the temperature of the stove falls so that no dilution is necessary and when the temperature falls to about 950 F. the blast is shiited to the next stove and the cold air valves again opened. It has never been considered feasible to run these stoves so as to afi'ord an end temperature much above 1200 F and even this is attained only with excessive waste as the heating and blowing have to be alternated more frequently and the minimum temperature of the escapng' gases is correspondingly ncreased thus decreasing the thermal efiiciency even more severely. Moreover each stove costs between &560,00000 and $100,000.00and requires constant *e1.n1iring,; ,amounting in efi'ect'to tri- Weile'the fourth stove is being repair' only three of the stoves are in operation;

Acco1'dingly`the detailed object of my present invention 's the provision of recuperative apparatus for blast furnace or open hearth furnace use or by-product'coke installation or the like which shall fit the interiors of these established regenerative stores, operate with the same valves, blowers,'pipes, and chimneys, compare favorably in cost with the present apparatus; require' less rcpairing, economize a greater propor tion of the heat,`deliver air to the point of use at a higher temperature, and maintain that temperature more uniform. Another object is to enable a decrease in thei number i of stoves, by enabling each stove tobe oper-- ated continuonsly, dispense with the need for diluting the efiluen't with cold air, and permit the abandonncnt of many of the valves, cross-connections and automatic temperature regulating devices heretofore used. Another object is to design 'the apparatus in such' wise that commercially available. metals can be used within their proper strengths under the different temperature conditions to which they are subjected without anywhere employing unnecessarily expensive materials; also by increasing the speed of operation of the blajst fnrnace to decrease the overhead costs and therehy effect the'reduction at a lower price per pound; while' further objects and advantages will become apparent as the description proceeds Two important priciples of my invention are:

(a) The hot and cold gases must flow concu-rently adjacentthehot end of theapparatus for protection of the mechanism and countercurrently adjacent the cold-end for completeness of heat absorpfr-ion;

(b) All metallic member h'ch, come in contactwith hot gases must depend from a fixed connection at the top and be free to move at the bottom sincethe only available metale have sa greater tensile strength at high temperatures than they have rigidity of form;

A corollary of these principles is:

(c) The air or gas being heated should flow vertically in an unbroken direction, while the waste gases should have a broken path, first upward and then downward (or vice versa). t

The first of these principles constitutes the essential subject-matter of my copending application filed March 2, 1921, Serial No. &49,172 The present application consitutes an improvement thereon in respect of cer tain features connected with the practice] large scale employmcnt of that principle.

In the drawings accompanying and form-' ing a part of this application I have illustrated certain typical emhodiments of my invention as applied to blast furnece regenerativ stoves. Fig. 1 is a central vertical -sectional view through such a stove containing my improvements, together with its exhaust fiue or chimney; Fig. 2 is a vertical central sectional view of the upper part of a similar stove equipped with a slightly modified form of my apparatus; Fig. 3 is a vertical central sectional view of the bottom part of a stove showing another slightly modified detail of my invention'; Fig. 4 is a horizontal sectional view corresponding to the line 4-4 of Fig. 3; Fig. 5 is a central vertical sectional View through the uppe' part of another blast- .urnace stove showing another detal modification; Figs. 6, 7, 8, and 9 are detail viewsof the lower ends 'of the heat transfer pipes and the mode of connecting same to the manifolds; Fig. 10 isa horizontal sectional View corresponding to the line l0-l0 of Fig. l; Fig.`11 is a horizontal sectional view corresponding to the line 11--11 of Fig. 5; Fig. 12 illustrat-es another mode of supporting and arranging the heat transfer pipes; and Fig. 13 is a horizontal sectional 'view of yet anothcr arrangenent of stove interior.

Describing the parts by reference characters, 1 denotes the exterior shell or casing of a standard blast urnacc. regenerative stove which is generally cylindrical in shape with a diameter of approx-imately 22 ft. and a height of apprpximately 100 ft. Its `upper end is surmounted generally by a curved cap 2`and its entire interior is lined with refractory brick 3 cfroineighteen inches to three feet in thickness.

Inside the cylindrical chamher de eter of the eeeeie inlicetecl et 4 in Fg. 1 sindi* clefining ?in eX- ter'ior ennulendowndrat chamber "5 ami en internal cylindricel upclreft chamber 6 ln the bottom of the chember 6 are' located the p'ovisions :for burning the blast fun `.heee gas, shown as comprsino en upright sidemhle height. Preferebly the chimney 4; a

extends to comperatively near thetop of the stove. do not limit; myself to the use of en exheust fan since the pressure under which the air and gas ere injectecl is often adequate to): their ejeotion but the' low :n-'el uniform temperature of the weste gases permits the use oi" common steel blowers at 13 and the requisite draft, een be obtained .much more cheuply bythe use of inechenical applicatiene then hy natural draft.. Besicles this permits 'the ubstraction of even more hent :hmm the wuste guses es will be shown.` Such en exheust fan is particularly useful when my improved reoupecatve stoves are used in connection with open heerth furnaces.

lldjuoent to the top ot the stove I locate u, suituble nunifold which in'ths particular instelletion serves the double purpose of colheating the heotecl air end supporting the pipes in which it is heate& In the form .shown in Fig. i this menfold is shown. at 15 end is ennuler in shupe, its outer diameter heing create' then the exte'ior cl iama 'himney i and its internal duam eter heing less thenthe internal diameter of the ehimney This maniltold communicetes with e brenchecl dischurge pipo 16 which in turn communieates with e suitable Conduit l? hei-e shown es emerg ing from the top of the Steve enti leading &henes (town- ?Ferdi? and leterelly to the hiest furnace plot shown) Formecl vin the uppec surtee of the menifohl 15 ere e plui'ulity of engulerly spececlepertuses .18 eech referehly fiaring upwewly es shown in ig. i enti receiving the eo'esponiihgly tepered lowntu-ned ende of gooee-uechs 10 formed et the uppeu ende ot' ppes %O -which depencl yertieell into the chamber 5 uncl other pipee 21 whic depenli into the chemher 6. The mezit'olcl is supported in lece in any suitable or desired menner. in 4 ig. 1 l have shown it es testing on en erch E t of retmc- -tjocy brick built m the upper emi of the stove, this arch being formed with suitable epertures 25 for the passage of the clfifei' ent ppes. Such an arch is preferably, en played in any case in order to shield' the menifold and the upper ends of the' -pipes from the direct contact of the hotgas, 'jlthough its supporting` function can be more' hereat'ter be shown. The manfolcll, pipo 16, pipes 21, and at least the upper'endsof' pipes 20 are made of alloys of chromiun prefembly containing approximutely: i 7

Chromiim between 14% and 18%! Nickel between 30% and 38%. 'Silicon between 'and 2%, &ndihej balance chiefiy iron; although it is of cou sef possibleto omit some 01' all of the silicon and substentially vary the proportions ofch'ro-` nium, nickel, and iron, although the alloysj made within the range described eXlibit a greetly increesecl` strength et hightn peratures which is the most ditlicult'quality to secure in apparatus of this character( However, 'by employing the features ofin--I Vention which I have set forth hereinfit ;be comes possible to use some of the oth 'f alloy's of chromium with iron group metale which would otherwise be too Weak for use For example, While the alloy first described is highly resistent to oxicltion it is 'not ;so immune to highly sulphurous gases and certen netailic :t'umes es are some of the othep chronium alloys such as c- 25 Fe 75, which, however, erecomparatively Weak athigh az; temperature& i The lower ends of these pipes are con- 3 nected to suitable 'manfo1ds, preferablyet points Well below the outlets 12 and burner;

'or less delegated to other devices as will the outer manifold is shown ut. 26,2ndg

he inner manifold et 27, both beingcon-j u blowd'r, 2??? by. which air is supplie& The

pipo 28 preferably has en internal diameter( of between three and four feet and the blower nust be able to deliver at least about:: 50,000 cubc feet of air 'per minute. i If 10 it s clesred to heat this air to a temperature of 1200 F. 'for delvery to the blast furnacc' it is necessary to &ftoi-d approximately 20,000 square feet of heat transfer'ring sur face, in contact with the hot gases, it being assumecl that the temperature of the cham-:- ber 6 at the mouth of the burne' Tisap proximatel 2600 E and the temperature* at thefiues 12 is epproximetely 200 F. `'If the issuing air is to be heated to a, lower-'12 temperature, or the escaping waste geses f are discharged ut a higher temperature e" smaller' amount of heet transferring surface 9 ported by a saddle 30 and is fot-med oppo-" site each of the tubes 21 with an annular pocket 31 containing mercury or other liquid, thus sealing the joint while permitting expansion and contraction of the parts which amounts to about six inches between extreme teinperatures. Another mode is shown in Fig. 7 wherein the manifold 527 likewise rests on a saddle 30 but instead of a mercury seal is formed with a packing gland 32 engaging a soft packing 33 which enga e the pipe 21 slidably, thus'producing a sli ing joint. In Fig. 8 the manitold 27 is provided at one side with a packing gland 34 adapted for the reception of hard packing 35 tightly gripping the pipe so that the manifold is supported out of contact with' the ground by the joint action of all the pipes and rises and falls therewith.

In Fig. 9 the manitold 27 is formed with nipples connected to the pipes by flexible hose which can even be of canvas when the temperature of the entering air is low. In the form of the device shown in Fig. 1 the lower ends of the chambers 5 and 6 are separated from the upper portions of the same y by suitable arches 36, and never reach any elevated temperature. If cold air be forced ,into the pipe 28 these chambers are cool :it

all times. The pipes 21 become very hot inside the chimney i although the concurrent direction of fiow protects them from becoming overheated and quickly reduces the temperature ot the burning gases to a point where they are no ,longer harmful to the brick work. By thetime these gases come in contact with the arch 24 and pipes 20 they are generally cooled at least to about 1200-1400 F. Only the upper ends of the pipes 20 need ordinarily to be of heat resistant material since common iron or steel materials are generally satistactory tor the lower ends thereof. The best design is that wherein the air euters the manifold 15 at the desircd temperature from both sets of pipes, although this requires a very much greater number ot pipes in the chamber 5 than in the chamber 6, and it is ractically satisfactory 'if the mixture o the two gases possess the proper temperature, the waste gas escapin through the fiues 12 being reduced to a suffieiently low temperature, and suflicient air at the same time introduced by way of the pipcs 21 to protect the latter against overheatng. wingto the fact that the hottest parte-of all the opipes depend verticaily from supports at their upper ends, the apparatus exhibits a minimum tendency to deformation.

'Dhe heatecl air issuing from this stove-e`sj hibits a constant temperature and the tem perature of the waste gases likewise remains constant and comparatively low degree, though seldom below 200 to 300 F. `Accordingly it becomes possible. still further the temperatures are so' low that metals of the cheapest nature can be successfully used for the purpose,` and the gases Carry very little dust or Corrosive substances. rangement for affecting this is shown at the right of Fig l wherein the lower .part of to extract some of this heat if desired since ne arthe chimney 14: is filled with econemizer units, each consisting of a 'pair of holiow' the inlet 42, and in this manner the fine` gases cooled an additional 100 which is equivalent to nearly two tons of coke per day. This saving'merely requires the economizers to be attached to the intahe of the `fan 29 and also preferably of the fan 10. In Fig.- 2 I have shown another mode of supporting and arranging (the pipes. The upper end of the chimney 4: is torned with laterally opening apertures 4 thus allowing the manifold to be set on top of the chimney. The manifold here shown consists of a cylindrical central section or hub, having a flat bottom 45 and cylindrical side walls from which radiate the hollow arms- 47. The pipes 20 and 21 depend from the bottom walls of the hu'b and arms, being fiared inside the same as in boiler making. A manhole 48 permits the entrance of a workman. Obviously this manifold could be supported above an arch if desired, al though this form of attachment .is rather best suited of any for direct contact with the hot gases and the manifold constitutes a further heating surface. l

In Fig. 3-1 have shown a' modified ar? rangement of inlet and outlet fines. shell 1, lining 3, chimney 4 and chambers 5-6 appear as before but the gas inlet 'assage 8 is elevated to a greater height iile the gas outlet 'passage 12' is lowered to ground level. The bottom of the` chimney is traversed by an arch 36 which separates the incoming and outgoing gas streams defining a shallow chamber -underneath, the

The

thrust of this arch being' supported by 'ial'- row radial arches orflying buttresses 50 which traverse the chamber 5 butwithout mesme closing passage through the same. The lower end of the chimney 4 is formed with arch ways 51 establishing communication between all parte of the bottom of the stove, Secured to the lower ends ot' the tubes -20 is :in annuler manitold 26 which,

v when the tubes are .staggered as herein in connection with Fiat. 1.

shown, is preferably made fiatter and wider than shown in Figggal and also' because of the fact .that this menifold lies in the path of the escaping gases, -is preferably Secured. tightly to the ppes as indicate& n F ig. 8 owing to the heat to which it is subjeoted which would likely injure any slip joint. The manifold 27 is referably Secured to the pipes ill- 21 in t e same manner and when these pipes also are staggered it is similar-ly made of flattened section.

The constructions heretofore shown require the discharge of the heated air at the top of the stove which is prectically feasible though sometimes inconvenient.. To cover the latter class of cases I have in Figs. 5, 10, and 12 illustrateddevices in which pro- Vision is made for the return movement of 'the heatedair inside the stove itself. In Fig. 5 thechimney e is made with vertical passageways 54 therein extendng throughout its' whole height; or the chinney may be consider-ed as made of two concentric walls spaced apart which is` another way of saying the same thing. Located at the upper end of the stove is a msnifold 15 having Secured thereto pipes 20 and 21 as described L I` have shown this manifold as shielded froni the direct action of the hot 'ases by means of a fire brick arch 249, although in the present instance this arch is relieved from all sup porting function, the manfold being sustained by suitable suspending provision's suitably connected to a treme work 56 located outside of the heated area. i

Secured to the bottom wall of the manifold 15 are a plurality of depending verti-- cal discharge pipes 57 which pass through the passageways 5& to any suitable outlet provision (not shown) at. the base of the stove. The entire pipe 21 requires to he made of heat resistant alloy, and also the upper ends of the pipes 20 and 57. In, case the temperature of the air delivered by :the stove is not over 900-l000 F. it is often possible to make these pipes of' e cheaper' material beginning' at some point below the top of the chimney tespecially the piges 20 which depend into a. region 'of gra .u ally decreasing temperature. The pipes 57 howeveg retain a suhstantielly uniform temperature between the increasing temperature on the inside and the decreasing temperature on the outside. It should he remembered, however, that ordinary steel exhihits at 1000 F. only approximately one-fifth the tensle strength it has at room temperature,

ture and 4000 lbs. per square inch at 1400?.

F. while steel cannot be subjected to any ep preeahle contnuous Stress et the last named.

temperature.

In Fig. 13 l have shown another arrangement for returning the heated gases where- '111 the chimney is made in the form of' two concentric cylindrical shells 4: and & spaced apert to define an ennuler combustion chamber 6 Inside the innermost shell' is located a vertical downdraft pipo 17 through which the heated air is withdrawn while the heat transfer pipes 21 continue' to occupy the annular ehainber 6 and the pi s 20 the outside annular chamber 5. "lhe ppe 17 should be made of heet resistant metal throughout furthernore this pipe exhibits a certain degree of ahsorbing function throughout since the chi-mney shell which surrounds it is more highly. heated at all times than the air inside this pipe.

In Fig. 12 I have shown another arrangement for supporting the different pipes wherein 60 represents a chamber' substantially like thatshown in Fig. 2' and*'61:' represents hollow arms of heat resistant' metal 'projectingtherefrom and formed at* sced ra'dieting.

their outer `ends' with fingers 62. Each of these 'gers is formed on its uppei` surface with' e plurality of holes in whichthe goose necksare seatecl.

In practice the dependingfipipes can be made of :fairly thin metal and t is found that the total weight of the interier parts of the stove is s ubstantially less than when 'the same is constructed in the `usual manner. Each stove 'constructed in' this way costs but little ifany more than the co`nstruction usuallv employed and iscepable of being used almost indefinitely., In order to provide' for inspection and repair I. adr Vocate making these stoves in pairs', or, when they are built by remodeling the existin type of' gas furnace reg'enerative stove,` advocete using onl stood, however, that I do not limit *mxself* to the Construction of my improved econonuzers m i abendoned. regeneratve stoves u since even better' results can 'be achieved with specially designed devices.

I have shown the parte inside the casing I th. two stoves which are near-est to the c mney for this particu as symmetrically arranged since this isnost 7 conducive to equality of beat expanson and is most convenent with a circular chamber,

but I do not confine myself tocircular-chambere nor to a symmetrical' arrangement.

N either do I in all cases limit myself to mi arrangement of the pipes ?in vertical position, nor to an arrangement of the pipes arallel to' the flow of the hot gases, although under the extreme conditions met in the specific use herein described these arrangementshave large practical advantages. Also I have shown the vertical wall which separates the updraft and downdraft chambers as circular in shape constituting a per ends, means for delivering heated gases to the bottom of one chamher and discharg-` ing such gases from the bottom of the other chamber, upwardly extending conduits of heat-conducting material located in both chambers, and means for .causing an upward flow through all said conduits of the gases to be heated. i

2. Preheating or recuperative apparatu's for gases comprising a pair of hollow upright chambers communicating at one end, means for delivering heated gases to the non-communicating end of one chamber and withdrawing the same from the non-communicating end of the other chamber, longitudinally extending conduits of heat conducting material in both chambers, and means for causing the gas to be heated to flow through such conduits in the same 'direction with the heated gases in the hotter chamber and in an oppposite direction from such gases in the cooler chamber.

3. Preheating or recuperative apparatus for gases comprising an upright chamber, vertically disposed conduits of heat conducting material Suspended in said chamher, a manifold connected to the lower ends of said conduits, said manitgld having aga's connection adjacent to the lower end of said chamber, means for causing hot gases to flow lengthwise of said chamher outside of said -conduits, and means for causing gases to be heated to flow through said conduits.

4. Prcheating or recuperative apparatus for gases comprising a pair of elongated parallel chambers for heated gases communicating with each other at one end, means delivering hcated gases'to the non communicating end of one chamber and withdrawing` such gases from the non-communicating end of the other chamber, longitudinally extendng conduts of 'heat condueting material posite ,to the flow of the heated gases in the cooler chamber.

5. Preheating or recuperative apparatus for g ases comprsing a hollow vertical heat .resistant shell, an upright chimney in said shell and defining chambers inside and outside the same, means for delivering heated gases to the bottom of one chamber and discharging such gases from the bottom of the other chamber, upward'ly extending conduits of heat conducting material located in both chambers, and means for causing an Upward flow through all said conduits of the gases to be heated.

6. Preheating or recuperative apparatus for gases comprising a hollow vertical heat resistant shell, an upright wall in said shell' and defining therewith an updraft chamber and a downdraft chamber, means for heating the lower end of one chamber, means for discharging spent roducts from the lower end of the other c ambel', a plurality of metal pipes Suspended at their upper ends and depending vertically into said chambere,

means for introducing gases to'be heated into .the lower ends of all said pipes, and

means tor carrying away the heated gases from the upper ends of said ipes.

7. Preheatng or recuperatve apparatus for gases comprising a hollow vertical heat resistant shell, a vertical chimney in saidshell and spaced `from the walls thereof, means fon introducin combustible material to the bottom of sa chimney, means for discha'gin'g spent combustion' roducts from the lower end of said shell, t e interier of said chimney communicating with the chamber surrounding the same only at the top, a hollow manifold of heat resistant material located above the top of said chimney, metalpipes depending from said manifold both into said chimney and into the chamber surroundin said chimney, manifolds connected to-the lower ends of said pipes, means for deliverin the gasesto be heated to said last manilolds and means for conveying away the heated gases from -said first manifold.

8. Recuperative ap'pa'ratus adapted for introduction into existing blast furnace stoves comprising a vertical chimney of refractory material extending from the bottom thereof to'a point near its top and spaced from its wall to define an annular chamber, the interior of the flue constitutng a combustion chamber and the exterior a downdraft ehamber, a manifold of heat downdraft chamber, means for forcing air v said shell to a 'point near its upper'end and tobe heated into the bottom manifglds, and means for conveyin the heated ga`ses away from the top mani old. 9.`Recuperative apparatus comprising, in combination, a as combustion chamber, a chamber throug which the combusto'n roducts are passed, means includingconuits of beat conducting material located in said chambers and a pump connected to said conduits in forcing relation for reducingthe temperature of said products below red heat, a third chamber through which the combustion products pass, and other conduits of heat conducting metal located in said last chamber and connected to the intake of said pump fofabstracting further heat units.

from said combustion productsfi 10. The combination with a blast furnace stove and its chimney, said stove' comprising a hollow shell lined with refractory ma-' terial 'and said chimney being connected to said shell nearits-lower end, of a chmney of refractory material rising inside sad shell to a pont near its upper end and con` stituting a combustion chamber, means for introducing combustible gas into thelower end of said last chimney, the space around, said last chimney constituting a down draft chamber, metallic conduits 'n said Cham` bers, andpum means for forcing air, upwardly throug all said conduits. a

11. The combination with a blast furnace stove and its chimney, said stove comprising a hollow shell lined with refractory material and 'said chimney being connected to said shell near its lower end, olta chimney of refractory material risirg inside constituting a combustion chamber, means for introducing combustible gas into the lowef end of said last chimney, thespace around said last chimney constituting a downdraft chamber, metallic conduits in said chambers, 'pump' means for forcing air upwardly through all said conduits, other conduits of sheet metal in said first chimney, and connections between said last conduits and the intake of said 'pump means.

12. In recuperative apparatus, achamberedstructure constitutng an updraft pase sage and a downdraft passage for'gases from a furnace, a plurality of Vertical con` duits of heat conductingnaterial located in both passages for the gases to be heated, means for forcing gases to be heated'in an upward direction through all of said conduits, means for mixing all such last named gases after passing through their'respective conduits and a mechanical exh'ast 'deyice' er constitutinga 'passageway exhaust device connected to the outlet fromsaid'chamber, a discharge chamber into which said exhaust device deli'v's, metallic hoat-transfer pipes in said .last chamber, and a pumping device having' its intake connected to said last pipes and its outlet connected to said metallic conduits. 14. Preheating or recuperative apparatus for gases, comprising a hollow uprght heat resistant' shell an`d a plurality of metal ipes" Suspended from their upper ende an de pending from their' upper ends. and de 'ending vertically inside said shell, a disc arge.:

manifold communicatin with the upper ends' of said pipes,` and exible sup ly connections for the lower ends of said ipes`, said connections extendin out throug the lower portion of said shell. V i

15. The method of preheating air by heat' interchange with hot combuston products which is characterized by subjecting a portion of the coldest air to the action of the hottest portion of the combustion products whereby the 'apparatus is shielded from injury, and subjecting the remaining portion of the coldest air to the action of the coolest rtion of the combustion products whereim by the maximum amount of heat is ab- 'stracted therefrom, and subsequently mixing thetwo portions of air. v

16. Recuperative apparatus for industrial high temperature uses comprising Cham bers for t e heated waste gases, conduits of heat conducting material *for the gases to be heated Suspended vertically in said. chambers, power exhaust' apparatus for such waste gases, and power pum ing apparatus for the gases to be heated, t e flow of the' gase to be heated being arranged to cool said conduits so as both to protect the same from the heat of the' waste gases and also to cool suchwaste gases 'sufliciently to shield said exhaust apparatus frominjury.

17.' Re'cuperatve apparatus for blast fur-= naces comprising conduits of'heat conduct ing material located inside the chambe'r of theexisting type of blast furnace regexerative oven, and 'means for forcing air to bewarmed throu h said conduits whereby 'the same is heate to a temperature great-er than- 1000f Fahrenheit and the conduits themselves protected against injury.

, l ;In testimony whereof, I liereunto aflixiny signature. v i

FRANK A. F HR NWALD 

